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Jim K - valve seats

14K views 15 replies 7 participants last post by  FMG_V6_btb 
#1 ·
or anyone else for that matter. on page 32 of your book we're talking about using a 30 deg stone to face the seat then lightly using a 45 to get the proper width. Nothing is mentioned about the outer diameter of the seat being cut so does the seat area extend all the way to the inside diameter of the valve seat face? The 45 stone decreases the seat width but how far from the edge of the valve should the seat area begin. I always thought the seat area should be in the middle of the valve seat face? Could someone please post a photo of what a proper valve seat on the valve should look like, seat would be great as well.
I'm asking because I just used a highly recommended machine shop and the intake seats look right, after lapping the seating area is in the middle of the valve face. BUT the exhaust seat is at the top of the valve seat face, I don't feel good about this at all. I took it to this guy and said I'd put the head back together myself to save money but I really wanted to see where he put the seat area. A photo would say a thousand words:) These are the std 30 deg valves btw.
Thanks!
 
#2 · (Edited)
SEAT width: 1 mm intake, 1.8 mm exhaust (approx.)
Don't confuse seat ring with SEAT (the contact surface), or SEAT, the car brand;)
Ah! the seat must be at the edge of the valve (external edge)
 
#3 ·
Mike, how wide is the seat in the head i.e., how much actual material is there from edge to edge? If you want the valve to seat further in you machinest ought to be able to do that. You really don't need more than a .050 or 1.8mm or so for an exhaust seat. Also there's been discussion about counterboring the seat .050 and using a 30 degree seat without the 45 degree cut.

Why don't you post a photo so we can see what you're doing?
 
#4 ·
Thanks, I've got the book, both the factory and Jim K's, I'm talkig about where the valve contacts the valve seat. Got the specs on how wide but Jim's book kinda confused me (which isn't hard to do). He says to cut a 30 and then cut a 45 on the inside to get the correct width. Where I'm losing it, does the 30 deg cut contact the valve face to the very of inside edge of the valve face? If you do what he says it seems it would and that doesn't sound right unless the valve seat is smaller in diameter than the ouside diameter of the valve.
After lapping the intake valves (the machine shop didn't do that which raised a red flag) the contact area is about 1 or 2 mm wide right in the middle of the valve face.
The exhaust valve after being lapped shows a tiny bit of lapped area right at the inside edge of the valve face. I know that's not right and I'll be having a conversation with the maching shop Monday.
My main question is that in the book Jim does not mention cutting a third angle on the outside of the valve seat to bring the seating area down the face of the valve to get the correct width of seating area. He only mentions cutting a 30 deg cut then the 45 for the inside. What about the outside. He does mention three cuts on using BMW 45 deg valves but not on the stock 30 deg valves.
(it's raining like hades right now and they are in the shop so i'll have to post a photo later. If someone has what one is supposed to look like I'd appreciate that and how they got 1 -2 mm with only two cuts. Thanks
 
#5 ·
Mike, what I meant was this: the counterbore is done at a right angle to the seat and, therefore you, don't need the 45 degree cut. I know JimK prefers to have more of a radius but, I agree with RJ (and also John Shankle from long ago) that counterboring is a good alternative. For one thing it opens up more of the valve throat which will be clearly evident once you've made the counterbore. This is especially effective with a 30 degree seat because of the shallower angle. All I did with mine was to lightly chamfer the edge of the counterbore with a stone. You are already departing from JimK's approach which uses a 45 degree valve seat. Keeping to a 30 degree seat and counterboring is a good alternative, IMNO, and may save you from putting in a new seat.
 
#6 · (Edited)
I understand this is really hard in the spoken word. I understand that a 50 counterbore is an alternative to the 45 deg cut to get the outside edge of where the valve contacts the seat. In Jimk's book he describes two ways to do the valves, one with a 30 deg seat and a 45 deg cut or as some do a 50 counterbore. The other way being with 45 deg valve faces. Since I'm using stock valves my question is what determines where the contact area ends as you go towards the outer edge of the valve? He only mentions making two cuts, first a 30 deg stone that is cut to the OD of the valve seat. Then a 45 which will give the beginning of the seating area on the inside edge of the valve but the way he describes it in his book is that the 30 deg cut goes all the way (or that's how I read it) to the edge of the valve seat which would be a very wide contact area. It would seem to me that a third cut of less thatn 30 deg would be required on the OD of the valve seat to bring the contact area away from the outside edge of the valve and give one the corrrect width of contact. He doesn't mention that so am I to assume the seat area goes to the edge of the valve?
In the photos below the intake valve seat area seems good to me but look at where the exhaust seat area is, all the way up the face. That cannot be right. It's quit raining:) The photo of the ex valve seat really doesn't tell much but it might to someone.


 
#8 ·
Thanks, I hope so, in any event I know where I'll be tomorrow at noon when he opens.
Here I have dyed the seat and lapped the ex valve. I really hope this guy has not killed my valve seats. He's not my usual machine shop guy but a really good mechanic who owns a shop highly recommened him. I know it ain't right but my original question for Jim K was why only two cuts on the seat? If you cut the 30 as wide as the seat (which is my interpertation of what he says in his book on page 32) the valve should contact it all the way out giving one a really wide contact area. He just mentions using the 45 on the inside, what do you do about the outside?


 
#9 · (Edited)
Intake:
-Angle: 30º
-Outer valve diameter: 44mm
-Seat width: 1.25 mm (for example)
-Calculation: 44 - (2 x (1.25 * cos 30º)) = 41.8 mm internal seat diameter.

Exhaust:
-Angle: 30º
-Outer valve diameter: 40mm
-Seat width: 2 mm (for example)
-Calculation: 40 - (2 x (2 * cos 30º)) = 36.5 mm internal seat diameter.

So once made the 30º cut, you have (if you have decided to take this way) to cut the seat (inside) with the 45º tool until the internal diameter of the already cut 30º seat reach the above indicated values.

The seat angle in the seat ring has to go beyond the external edge of the valve, so the seat contact surface start at the very edge of the valve.

Note that this is a 2 angle job, not a 3 angle job which is useless in this engine due to the combustion chamber shape around the valves (spherical). The airflow will have a first deviation of 45º:eek:, after a 15º deviation when flowing over the seat, and after another 5º to 10º to the combustion chamber rounded wall, so why to put a 3rd angle in this last section?.
 
#10 ·
I see your point. I've just never heard of seats that extend to the edge of the valve face. I can see how that is great for optimum air flow but if the seat area is at the edge of the valve which is the thinnest part of the valve then what does that do to longevity? I've always been told the seat area should be in the middle of the seat face or slightly towards the outer edge like the photo of the intake valve which would be a compromise between optimum air flow and longevity. I'm not trying to argue but to get a good understanding of what works best for a modified street motor. I've ported the head and manifold to Jims specs, 11 lift cams, HD valve springs, modified guides, motronic pistons, and an Ingram HP spica pump.
 
#11 ·
machine shop gladly put the seat on the exhaust valve like it is on the intake. Couldn't buy into the seat going all the way out to the edge of the valve face.
 
#12 ·
Seat design

the proper cut is to open the seat with a 75 degree cutter and leave .040, 30 degree seat at the outer margin of the valve. No durability issues unless your valves are cut with thin margins. I also reshape the back & front of the new valves for flow.

3 angle cuts are for grandmothers car.

A 45 degree cutter can be used only to break the lip of the interface of the 75 degree and 30 degree cuts. The 30 degree cut should be done AFTER the new guides are installed and reamed to size. Then the 30 degree will match where the valve now sits with new guides.:p
 
#13 ·
That's what we did, thanks for the confirmation! I still would like to know if JimK's book would put the seat all the way to the edge of the valve. That's how I read it. he says hit it with a 30 deg all the way to the edge on 30 deg seats, just doesn't make sense to me which is why I was trying to get a hold of him so he could explain to me exactly what he was saying.
 
#14 ·
What I prefer to see: If a valve is 46mm, the outside edge of the 45* seat on the head should be 45.5mm, this also being the inside edge of the 30*cut (if you have one, which is nice). Seat width should be as specified for in/ex and then its 60* followed by 75*. If you have a special radiused tool to do all-in-one, so much the better. I put my own guides in and finish my own seats after the machine shop puts in bigger ones. The sequence is: large seat insallation (and left uncut), head ported, guides installed, seats cut and detailed.
Jim K.
 
#15 ·
Would this be the same for Twin Spark Intake Valves of 46mm and 47mm?

Is there a downside to the bigger valves ?

Does anyone have a diagram of how the cuts end up . The diagram on page 31
of Jim's book shows the standard and a modified seat for a standard valve .

I found this not sure what it motor it's for.

Diagram Text Line Font Design


With the larger valves the 30* becomes a 45* and the 45* a 60* ???
:confused:
 
#16 · (Edited)
In black the angles for the 2.0 twin spark 16 valves, the red data is for a nord, but are wrong: the angle value in "a" belongs to the "Y" angle, and NONE for the "a" angle, but of course, you can put here a blend angle to better adapt the flow from the real seat angle to the combustion chamber wall.
 

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